OP, only just seen this.
With respect, IMO the argument re wrong contravention is itself wrong..but see below.
As far as can be seen, the restriction was imposed under a Temp Traffic Order, s14 RTRA refers.
7)An order or notice made or issued under this section may—
(a)suspend any statutory provision to which this subsection applies; or
(b)for either of the reasons or for the purpose mentioned in subsection (1) above suspend any such provision without imposing any such restriction or prohibition as is mentioned in subsection (1) or (2) above.
(8)Subsection (7) above applies to—
(a)any statutory provision of a description which could have been contained in an order or notice under this section;
(b)an order under section 32(1)(b), 35, 45, 46 or 49 of this Act or any such order as is mentioned in paragraph 11(1) of Schedule 10 to this Act
A TTO may suspend the application of any s45 TMO which designated the parking place and substitute a different restriction, in this case no waiting. The council could have chosen to simply suspend the parking place but chose to go the TTO route, for reasons which are probably explained within the order which tantalisingly is not in any of the photos albeit that it is key. At present there's no order in evidence, so IMO you could argue that the order did not apply to where you were parked i.e. it is the order which creates the restriction, not the words on a sign, and without that order being in evidence you challenge that the restriction applied and therefore that the contravention took place. If the authority reject these representations then they must produce a copy of the order relied upon with any response.